In this type of runner, the latch is generally provided with a plurality of teeth which serve, when the latch is in its locked position, to come to co-operate with series of cutouts formed in the moving rail, and with series of catches formed on the fixed rail so as to hold said moving rail to prevent it from moving relative to the fixed rail. Conventionally, the catches formed on the fixed rail are spaced apart uniformly at an identical pitch, thereby making it possible for the teeth on the latch to lock between the catches at uniform intervals, so as to enable the moving rail to be adjusted in as many longitudinal positions as there are catches on the fixed rail.
However, with certain types of motor vehicle seat, such as, for example rear bench seats, it is preferable for the moving rail to be locked relative to the fixed rail in predetermined longitudinal positions of which there can be three, for example, which requires the latch to be in the locked position in its predetermined longitudinal positions only. For this purpose, and in a manner known per Se, the fixed rails of such runners have catches that are not uniformly spaced apart so as to generate zones without catches and zones with catches, said zones with catches serving to co-operate with the teeth on the latch to define predetermined locking positions in which the moving rail is locked relative to the fixed rail.
It can thus be understood that, in order to obtain predetermined locking positions in which the moving rail is locked relative to the fixed rail, it is essential to configure the series of catches on the fixed rail to obtain zones without catches that form zones in which the latch cannot return to its locked position. This thus makes it necessary to manufacture specific sets of runners having catches that are non-uniformly distributed when it is desired for the moving rail to lock in a small number of predetermined longitudinal positions only.